Heat generating pipe

ABSTRACT

A heat-generating pipe arrangement employs at least one pipe of ferromagnetic metal, an insulated electric conductor line connected to a source of AC supply and inserted within the pipe throughout the entire length thereof and a good heat-conductive material such as water, sea water or the like which exists in the clearance space between the conductor line and the pipe. The pipe is heated by the alternating current flowing through the inner wall portion thereof on account of the skin effect, which is a return current from the conductor line to the source of AC. The heat-conductive material is effective in preventing the temperature rise of insulating-material covering the conductor line and reduces the cost of heat-generating pipe per unit of heat generation.

United States Patent [72] Inventor Masao Ando Kanagawaken, Japan [21]Appl No. 627,721 (22] Filed Apr. 3, 1967 [45] Patented July 6, 1971 [73]Assignee Chisso Corporation Osako, Japan [32] Priority Apr. 5, 1966 (33]Japan [31] 41/21393 [54] HEAT GENERATING PIPE 4 Claims, 2 Drawing Figs.

[52] US. Cl; 219/540, 174/15, 219/1049, 219110.51, 219/300, 219/301,338/231 [51] Int. Cl 1105b 3/40 [50] Field of Search 219/300,301,10.51,10.65,10.49,535,10.79, 530, 540; 174/28, 15 C; 338/231, 271

[56] References Cited UNITED STATES PATENTS 2,066,323 l/l937 Bennett174/15 (C) 3,170,026 2/1965 Woodson 174/15 (C) Primary Examiner-A.Bartis Attorney-Craig, Antonelli, Stewart & Hill ABSTRACT: Aheat-generating pipe arrangement employs at least one pipe offerromagnetic metal, an insulated electric conductor line connected to asource of AC supply and inserted within the pipe throughout the entirelength thereof and a good heat-conductive material such as water, seawater or the like which exists in the clearance space between theconductor line and the pipe. The pipe is heated by the alternatingcurrent flowing through the inner wall portion thereof on account of theskin effect, which is a return current from the conductor line to thesource of AC. The heat-conductive material is effective in preventingthe temperature rise of insulating-material covering the conductor lineand reduces the cost of heat-generating pipe per unit of heatgeneration.

ATENIEUJUL BIB?! 3,591,770

I NTOR. 0 ANDO ATTORNEYS HEAT GENERATING PIPE CROSS REFERENCE Thisinvention is concerned with an improvement on the apparatus disclosed bythe present inventor in the Japanese Pat.

No. 460,224 corresponding to U.S. Pat. No. 3,293,407.

BRIEF SUMMARY OF THE INVENTION DETAILED EXPLANATION It is well-knownthat when an alternating current flows through a conductor, the currentconcentrates on the surface of the conductor and shows a so-calied skineffect. When the skin effect is pronounced, the depth of the skin S(cm.) in which a current flows can be expressed by the following formulaS=5030Vphf (1) wherein 8 (OJ cm.) is a resistivity of a conductor, p. isa permeability and f (cycle/sec.) is a frequency.

When an alternating current is supplied to a conductor line insertedwithin a pipe of ferromagnetic metal throughout the entire lengththereof and the current which flows through said pipe is caused toconcentrate on the inner wall portion of said pipe by the skin effect,there will be substantially no current flow on the outer surface portionof said pipe so long as the relations expressed by the followingformulas l D wherein D (cm.) is an inside diameter of said pipe, 2 (cm.)is its thickness and l (cm.) is its length, are satisfied. When acommercial steel pipe is used as a pipe of ferromagnetic metal and analternating current of commercial frequency (50 or 60 cycles) isapplied, the depth of the outer skin calculated by the formulas is about1 mm. Accordingly, there will be substantially no current flow on thesurface of a pipe so long as its thickness is more than 2 mm. Thealternating current is supplied to the circuit consisting of aninsulated conductor line inserted within a pipe of ferromagnetic metalthroughout the entire length thereof and a return path, i.e., the metalpipe formed by connecting the end of the conductor to the end of themetal pipe, as disclosed in the specification of the establishedJapanese Pat. No. 460224, the current flowing through the metal pipe isconcentrated on the inner wall of the metal pipe on account of the skineffect. When a suitable thickness is selected for the pipe,substantially no electric potential appears on the outer surface of thepipe. If a heatgenerating pipe of this kind is used, there is no needofinsulation between the heat-generating pipe and supporting materi alsor material to be heated. There is substantially no leakage loss ofcurrent and no electric injury to human beings and animals even whenthey touch the pipe. The current which is concentrated on the innersurface of the pipe flows therethrough and generates heat by theresistance of the metallic material.

The heat-generating pipes disclosed in the above-mentioned patent can beused for heating various materials. Particularly they are suitable forheating transportation pipes or maintaining the temperature of suchpipes as those used for transporting materials or solutions whichsolidify or increase their viscosities, e.g. crude oil, heavy oil, solidparaffin, acetic acid,

naphthalene, aqueous solution of caustic soda of high concentration,etc. They are also applied advantageously to highspeed traffic ways inwhich snowdrifts and freezing are extremely harmful or to runways foraircraft because of simplicity, low construction cost, high reliabilityand easy maintenance.

An object of the present invention is to provide a heatgenerating pipewhich is improved over the ones disclosed in the above-mentioned priorpatent in durability, unit cost and readiness of installation. Thisobject can be attained by spacing the conductor line apart from theinner wall of the pipe throughout its length to form a clearance spacetherebetween and filling the space with a heat conductive materialhaving a conductivity higher than that of air. Another object of thepresent invention is to provide a heat-generating pipe which allows aliquid surrounding said pipe to enter its clearance space and utilizessuch a liquid as a heat-conducting medium. These objects and otheradvantages can be attained by the heat-generating pipe of the presentinvention.

One feature of the present heat-generating pipe consists in causing asubstance having a good heat conductivity to fill the clearance spacebetween the insulated conductor and a ferromagnetic pipe surrounding thesaid insulated conductor in the arrangement that alternating currentflowing through the said insulated conductor generates heat upon theinner surface of the said ferromagnetic pipe.

Another feature of the present heat-generating pipe consists in causinga liquid surrounding said pipe to enter the clearance space between theinsulated conductor and a ferromagnetic pipe surrounding the saidinsulated conductor in the same arrangement as mentioned above therebyto improve the heat conductivity between the conductor and the pipe.

The heat-generating pipe of the present invention is illustrated morefully by referring to the accompanying drawings.

FIG. I is a cross-sectional view of the present heat-generating pipe.

FIG. 2 is a schematic wiring diagram for illustrating the principle ofthe present heat-generating pipe.

In FIG. 1, l is a ferromagnetic pipe, 2 is an insulating materialcovering a conductor 3 and 4 is the clearance space between theferromagnetic pipe and the insulated conductor and filled with amaterial having a good thermal conductivity.

FIG. 2 is the connecting diagram disclosed in U.S. Pat. No. 3,293,407.In this FIG., 33 is an alternating current source and 34 is aferromagnetic metal pipe. An insulated conductor line connected to theterminal of AC source and inserted within said pipe throughout theentire length thereof, is connected to the end 36 of said pipe 34 remotefrom the AC source to form a circuit. When an alternating current issupplied to this circuit, the current flowing through the pipe 34 isconcentrated on the inner wall 39 of the pipe 34 and there issubstantially no potential appearing on the outer surface of the pipe34. Accordingly, even when such a heat-generating pipe is brought intodirect contact with a supporter thereof or a material to be heatedtherewith, the leakage of current from the pipe 34 into such a materialdoes not occur practically.

The foregoing is an illustration of the heat-generating pipe of thepresent invention with a single power source. It goes without sayingthat a multiphase alternating current as an AC source, and various kindsof wiring systems can be used in the practical application of thepresent heat-generating pipe.

The cost of the heat-generating pipe of the present invention dependsupon the cost of the insulating material. The allowable current in theinsulated conductor is decided by the allowable temperature of theinsulating material. When an alternating current is supplied to theabove-mentioned heatgenerating pipe in order to generate heat, the heatis mostly generated on the inner surface of the ferromagnetic pipe. Theheat is transmitted through the pipe wall and dissipated from the outerwall of the pipe. Even with the assumption that heat is not generated inthe conductor, the inside of the pipe shows the highest temperature.Besides this, conductors such as copper and aluminum which have beenwidely used on account of their low electric resistance, generate heaton account of their inherent electric resistance according to thestrength of the current. Accordingly, among the construction elements ofthe above-mentioned heat-generating pipe, the insulated conductor 3encircled by a ferromagnetic pipe 1 shows the highest temperature. Theheat generated in the conductor 3, conducts through the insulatingmaterial 2, reaches the outer surface thereof and further conductsthrough the clearance space 4 and reaches the ferromagnetic pipe 1.

The allowable current in the insulated conductor of the heat-generatingpipe is determined according to the allowable temperature of theinsulating material. Needless to say, the temperature of the insulatingmaterial depends upon the temperature of the inner wall of theferromagnetic pipe 1 and the heat conductivity of the material existingin the clearance space 4.

The temperature distribution in the heat-generating pipe of this kind isdetermined by measuring the temperatures in the conductor, in theinsulating material and on the inner surface of the metal pipe. inaccordance with measurements carried out on the present invention, itwas found that when the clearance space 4 is occupied by air, about 90percent of the overall temperature difference between the conductor andthe inner wall of the pipe occurs at the clearance space and theremaining percent, as little as it is, occurs in the insulating materialof the conductor; therefore, provided that the clearance space had nothermal resistance, the overall temperature difference could be greatlyreduced so as to be equal to the temperature difference between theconductor and the surface of the insulating material. As a result,compared with the former case where the clearance space was occupied byair, the latter case could be 10 times as large and the transmissionfrom the conductor to the inner wall of the pipe, and about three timesas large in the allowable current going in the conductor when the innerwall of the pipe is kept at a constant temperature difference isproportional to the heat quantity generated in the conductor, while theheat quantity is proportional to the square of the current flowingthrough the conductor.

Operation of the conductor at high currents is not practical. From theeconomical view point on account of voltage drop and power loss in thecommon power distribution, but as is readily understood from theconstruction of the heat-generating pipe, even the heat generated in theconductor can be effectively used without any trouble. In other words,the heat generated in the conductor provides for the saving of theamount of conductor necessary to generate a unit calorie and reduces thecost of the heat generating pipe.

Since there is no material having zero heat resistance, it is impossibleto make the resistance zero, but if the clearance space is filled with amaterial having a good heat-conductivity, the temperature differencebetween the conductor and the wall of the metal pipe can be reduced. Forexample, by comparing the heat transmission rate and heat conductivityof water, 1,000 Kcal./m., hr., C. and 0.54 Kcal./m., hr., C.respectively, with those of air, ca. l0 KcaL/mf, hr., C. and 0.023Kcal./m., hr., C., respectively, it is apparent that the former affordshigher rate of heat transmission than the latter.

As the materials which can satisfy the above-mentioned purpose, water,sea water, aqueous solutions of salts, fats and oils, mineral oils,glycols, aqueous solution of alcohol or glycol can be illustrated. Whenthe heat-generating pipes are used at relatively low temperature c.g.lower than 100 C., an inex pensive material such as water or aqueoussolution of slat is preferable.

Further the filling of the clearance space with a material having a goodheat-conductivity affords another advantage that when a high voltagecurrent is supplied to the insulated conductor 3, the electric fieldstrength on the outer surface of the conductor can be made uniform andthe life of the insulating material can be prolonged.

As for the insulating material covering the conductor line,

conventional materials such as various kinds of rubber, polyvinylchloride, polyisobutylene, Teflon or the like may be selected accordingto the service temperature. When the temperature is higher than C.,Teflon is a suitable material for the insulator.

When the present heat-generating pipe is used with a transportation pipeinstalled in water including sea water or in the underground water,further notable advantage can be attained by the use of theheat-generating pipe having an open construction. By such aconstruction, it is possible to utilize as a heat-conductive medium theliquid surrounding said pipe (the environment liquid), entering theinside of the heat-generating pipe and filling the clearance space.However it is necessary to pay attention to the construction of theheat-generating pipe so as not to allow the environmental liquid come inor go out of the pipe too easily thereby to cause the heat loss by suchmovement. On the contrary, when the heat-generating pipe is so long thatthe entering of the environment liquid from the pipe end isinsufficient, or when, due to the uneven configuration of the terrainover which the transportation pipe passes, a gas trap may be formed thuspreventing the environment liquid from filling the heat-generating pipe.It is necessary to use a means so as to fill the liquid in the entirelength of the pipe. For example, it is possibleito provide smallopenings .such as holes or slits in the metal pipe at suitable intervalsor to use a number of short independent metal pipes which are arrangedin series, electrically connected and both the ends of which are open. 1

When the present heat-generating pipe is installed in the air or in theplace where environmental liquid is not present, it goes without sayingthat the construction must be of the type which does not cause leakageof the liquid, i.e. the heat conducting medium, and vent parts must beprovided so as not to cause the gas to be trapped in the pipe.

When the present heat-generating pipe is connected to the material to beheated, by contacting or welding, a temperature difference is naturallyestablished between the contact part of the heat-generating pipe andother parts. However such a temperature difference is slight in thepresent heat-generating pipe and hence the life of the heat-generatingpipe can be prolonged and the heat insulation can be made simpler.

I claim:

l. A heat-generating pipe arrangement comprising at least one pipe offerromagnetic metal, a conductor line electrically connecting one end ofsaid pipe to an AC supply source, an insulated conductor line connectedto said AC supply source and extending through the inside of said pipeand being electrically connected to the other end of said pipe remotefrom said one end of said pipe to form an AC circuit and beingspaced-apart from the inner wall of said pipe throughout its length toform a clearance space therebetween, the clearance space beingcompletely filled with a material having a higher thermal conductivitythan air, said pipe having a wall thickness greater than twice thepenetration depth of the alternating current flowing therethrough,whereby the current flowing through said pipe is: caused to concentrateon the inner wall portion thereof by the skin effect and generates heatthereon without any practical voltage appearing on the outer surface ofsaid pipe.

2. The heat-generating pipe arrangement according to claim 1, whereinthe material having a higher thermal conductivity than air is a liquid.

3. The heat-generating pipe arrangement according to claim 2, whereinsaid liquid is water.

4. The heat-generating pipe arrangement according to claim 2, whereinsaid liquid is salt water.

1. A heat-generating pipe arrangement comprising at least one pipe offerromagnetic metal, a conductor line electrically connecting one end ofsaid pipe to an AC supply source, an insulated conductor line connectedto said AC supply source and extending through the inside of said pipeand being electrically connected to the other end of said pipe remotefrom said one end of said pipe to form an AC circuit and beingspaced-apart from the inner wall of said pipe throughout its length toform a clearance space therebetween, the clearance space beingcompletely filled with a material having a higher thermal conductivitythan air, said pipe having a wall thickness greater than twice thepenetration depth of the alternating current flowing therethrough,whereby the current flowing through said pipe is caused to concentrateon the inner wall portion thereof by the skin effect and generates heatthereon without any practical voltage appearing on the outer surface ofsaid pipe.
 2. The heat-generating pipe arrangement according to claim 1,wherein the material having a higher thermal conductivity than air is aliquid.
 3. The heat-generating pipe arrangement according to claim 2,wherein said liquid is water.
 4. The heat-generating pipe arrangementaccording to claim 2, wherein said liquid is salt water.